This invention relates to coordinated control for a powertrain with a continuously variable transmission. More particularly, this invention relates to coordinated control of a continuously variable transmission and an engine to provide improved acceleration and drivability.
Powertrains that have an internal combustion engine coupled to a continuously or infinitely variable transmission are used to provide efficient drive systems. In continuously or infinitely variable transmissions (hereinafter xe2x80x9cCVTxe2x80x9d), the transmission ratio can be changed in a continuous manner from a maximum under drive ratio to a maximum over drive ratio. This permits the engine to be operated at either the best fuel consumption area or the best performance area. Engine speed can be maintained at a substantially constant level while the transmission ratio is varied to attain a desired vehicle speed as requested by an operator.
Many different CVT systems are in use. For example, one such CVT is a belt drive CVT. Belt drive CVTs use a flexible belt that runs against steel sheaves. The sheaves of the input and output pulleys are movable axially to adjust the radius at which the belt turns, and therefore adjust the transmission ratio. A hydraulic pressure distributed from a control valve often moves the sheaves. U.S. Pat. No. 5,997,431 to the assignee of this invention provides such a hydraulically-actuated CVT, the contents of which are incorporated herein by reference.
The primary benefit of CVT devices is to let the engine operate independently of any load. This flexibility, in principle, allows the optimization of fuel economy without degradation of acceleration performance. But, optimizing the myriad of operating conditions has been difficult in prior control systems (e.g., uncoordinated control systems and decentralized control systems) of CVT powertrains.
In use of a CVT powertrain, movement by the driver of an accelerator pedal provides an indication of an amount of acceleration or deceleration. A supervisory control module then determines the desired engine and vehicle operating conditions that correspond to the acceleration command. Subsequently, one or more high-level control inputs drive the CVT powertrain to achieve the desired engine and CVT operation, while low-level internal controllers independently regulate the engine and CVT system behavior.
A method of controlling a vehicle is provided. The method includes controlling a continuously variable transmission and an engine with a supervisory controller and a powertrain controller; providing a driver input to the supervisory controller; controlling the supervisory controller to constrain the engine along a predetermined operating curve during a steady state condition of the driver input; and controlling the supervisory controller to relax the engine from the predetermined operating curve during a non-steady state condition of the driver input such that the powertrain controller coordinates an engine throttle and a rate of change of the continuously variable transmission ratio. Here, the predetermined operating curve is maintained by adjusting a continuously variable transmission ratio.
A control system for controlling a continuously variable transmission and an engine is provided. The control system includes a driver input, a supervisory control module, cross coupling inputs, an engine controller, and a transmission controller. The driver input has a steady state condition and a non-steady state condition. The supervisory control module constrains the engine to a predetermined operating curve in response to the steady state condition of the driver input. Moreover, the supervisory control module relaxes the engine from the predetermined operating curve in response to the non-steady state condition of the driver input. The cross coupling inputs are indicative of at least a portion of the steady state condition or the non-steady state condition. The engine controller receives a desired wheel speed, an actual wheel speed, and the cross coupling inputs. In response, the engine controller provides a desired engine throttle to the engine. Similarly, the transmission controller receives a desired transmission ratio, an actual transmission ratio, and the cross coupling inputs. In response, the transmission controller provides a desired CVT ratio change rate to the continuously variable transmission. The engine and transmission controllers receive the cross coupling inputs simultaneously such that the desired engine throttle corresponds to the driver input and the desired CVT ratio change rate corresponds to the driver input.
A method of eliminating a non-minimum phase zero effect from a CVT ratio change rate input to a wheel speed output of a continuously variable transmission coupled to an engine is provided. The method includes constraining the engine to operate along a predetermined operating curve during a steady state condition; relaxing the engine from the predetermined operating curve during a non-steady state condition; and providing cross coupling inputs indicative of at least a portion of the non-steady state condition.
A control system for a vehicle is provided. The control system includes a powertrain and a supervisory control module. The powertrain has an engine, a continuously variable transmission, and a two-input, two-output control module. The supervisory control module constrains the engine to an optimal engine operating curve in response to a first driver input, but relaxes the engine from the optimal engine operating curve in response to a second driver input. The two-input, two-output control module has first and second cross coupling inputs being indicative of at least a portion of the second driver input. The two-input, two-output control module receives a desired wheel speed, a desired transmission ratio, an actual wheel speed, an actual transmission ratio from the vehicle, and the first and second cross coupling inputs. In response, the two-input, two-output control module provides a desired engine throttle to the engine and a desired CVT ratio change rate to the continuously variable transmission. Thus, the desired engine throttle corresponds to the second driver input and the desired CVT ratio change rate corresponds to the second driver input.
The above-described and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims